Vinyl chloride resins have been widely used in various fields due to their excellent physical and chemical properties. However, vinyl chloride resins have various disadvantages from the viewpoint of workability. That is, vinyl chloride polymers have a high melt viscosity, a poor flowability, a narrow temperature range in which the resins can be converted to shaped products because the shaping temperature is close to the thermal decomposition temperature thereof, and a slow gelling rate. For these reasons, these resins are difficult to convert rapidly from a powdery state to a uniform molten state when they are subjected to a roll milling procedure and thus the resultant shaped product later has a degraded surface appearance.
The addition of a plasticizer to vinyl chloride resins in order to eliminate the above-mentioned disadvantages is well known. However, the use of a plasticizer creates some problems due to the plasticizer's volatility and also results in a decreased mechanical property of the resultant shaped product. Accordingly, a plasticizer is useless for producing a rigid polyvinyl chloride-shaped product.
In another attempt to improve the processing properties of vinyl chloride resins, various copolymers compatible with vinyl chloride resins are used as a processing aid to increase the gelling rate of the resins and to reduce the stickiness thereof to the metal surface of the molding machine used, thereby-increasing productivity, so as to obtain a resultant shaped product having a smooth surface, to impart a uniform luster to all shaped products produced when the molding procedure is continuously carried out for a long period of time, and to attain deep drawability in the resultant shaped product. Some of these copolymers are successful in some fields of application. Typical copolymers which are presently marketed are those which contain methyl methacrylate as a main component. These copolymers are effective for promoting the gelling rate of vinyl chloride resins and for increasing the tensile elongation of the resultant shaped product at elevated temperatures. However, these copolymers are disadvantageous in that a film extruded from a vinyl chloride resin having these copolymers incorporated therein is deficient in luster and contains a non-gelled material (which is also referred to as fisheye). These disadvantages detract from the value of the film. Also, the above-mentioned methyl methacrylate copolymers exhibit, in themselves, a high adhesion to a metal surface and have a high melt viscosity. For these reasons, when vinyl chloride resin compositions having copolymers consisting mainly of methly methacrylate incorporated therein are subjected to a molding procedure, a remarkable increase in torque (milling resistance) is encountered, resulting in a decrease in productivity. To overcome these defects, the use of a lubricant in combination with a methyl methacrylate copolymer has been attempted. However, the amount of lubricant which can be used is limited from the standpoint of retention of the physical properties of the vinyl chloride resin composition. In addition, even if a lubricant is used within the permissible range, the vinyl chloride resin composition cannot maintain its lasting lubricating property at a satisfactory level during the shaping process. Moreover, the use of a lubricant is disadvantageous in that the lubricant adheres to the surface of the mold during the molding procedure (this adhesion is also referred to as plate out) and causes blooming on the surface of the resultant shaped product. Accordingly, the use of a lubricant in combination with a methyl methacrylate copolymer is also ineffective for improving the workability of a vinyl chloride resin.
There have also been proposed vinyl chloride polymer compositions capable of overcoming all of the above-mentioned defects in one stroke, i.e., exhibiting an excellent releasing property from a calendering roll when subjected to a calendering procedure and a lasting lubricating property and producing a shaped product having improved fabricating properties, such as high tensile elongation at elevated temperatures, and an excellent deep drawability while retaining the transparency characteristic of the vinyl chloride resin. These compositions yield fairly successful results. However, some of these compositions result in an increase in deposits on the surface of the mold during the molding procedure. Accordingly, it cannot be said that these compositions satisfactorily meet the requirements in the art. Under these circumstances, there is a strong desire for a processing aid capable of further increasing the flowability and lubricity durability of a vinyl chloride resin when it is subjected to a processing procedure from the standpoints of an increase in productivity and quality and a reduction in energy.
The inventors of the present invention made extensive studies in consideration of the above-mentioned problems. As a result, the inventors of the present invention succeeded in obtaining a vinyl chloride polymer composition exhibiting an excellent flowability and a lasting lubricating property and which is free from the plate out phenomenon while retaining excellent processing properties possessed by a vinyl chloride resin having a methyl methacrylate copolymer incorporated therein. Thus, the inventors of the present invention attained the present invention.